It is common practice in the industry to form silicon dioxide films, either doped or undoped according to the particular application, on or as a layer in semiconductor devices. The literature is replete with discussions of the function of such layers and various methods of forming silicon dioxide layers. See, for example, Thomas, HANDBOOK OF TRANSISTORS, SEMICONDUCTORS, INSTRUMENTS AND MICROELECTRONICS, Prentice Hall, Englewood Cliffs, N.J. 1968 and the extensive publications of the J. C. Schumacher Company, e.g. Tetraethyl Orthosilicate (TEOS), Product Data Sheet No. 6; Tetraethyl Orthosilicate for Semiconductor High Temperature Silicon Dioxide Depositions, Product Application Note No. 8; TEOS and Liquid Dopant Sources for CVD SiO.sub.2, PSG, and BPSG, Product Application Note No. 15; Adams and Capio, The Deposition of Silicon Dioxide Films at Reduced Pressure, Technical Article Reprint No. 5.
Thus, the deposition of doped and undoped silicon oxide films is an important process in semiconductor device fabrication. The silicon source usually is a toxic and pyrophoric gas. The use of safer liquid sources is the goal of many investigators. F. S. Becker and D. Pawlik, ECS 85-2 (85)380, ECS 86-8 p148 "A New LPCVD Borophosphosilicate Glass Process Based on the Doped Deposition of TEOS-Oxide". G. Smolinsky and T. P. H. F. Wendling, JECS 132(85)950 "Measurement of the Temperature Dependent stress of Silicon Oxide Films Prepared by a Variety of CVD Methods". G. Smolinsky and R. E. Dean "LPCVD of Silicon Oxide Films in the Temperature Range of 410.degree. to 600.degree. C. from Diacetoxyditertiarybutylsilane". F. S. Becker, D. Pawlik, H. Schaefer, and G. Staudigl, JVST B4(86)232 "Process and Film Characterization of Low Pressure TEOS-Borophosphosilicate Glass". D. S. Williams and E. A. Dein "LPCVD of Borophosphosilicate Glass from Organic Reactants". The thermal decomposition of tetraethoxysilane (TESO) has been used for over twenty years to obtain undoped silicon dioxide films in the temperature range from 600.degree. to 800.degree. C., A. Hochberg and D. O'Meara "LPCVD of Silicon Dioxide Films from Tetraethyoxysilane". An excellent text on the various processes for deposition of thin films is Thin Film Processes edited by John L. Vossen and Werner Kern, published by Academic Press Inc., Orlando, Fla. 32887.
The development of a phosphorus doped film, using liquid sources, has been hindered by the lack of a suitable phosphorus source. Trimethylphosphate (TMPO) with TEOS does not provide more than 3 w/o phosphorus, while trimethylphosphite (TMPI) is too reactive above 600.degree. C. TMPO has been used with TEOS at lower temperatures to produce doped films.
A liquid source producing undoped silicon oxide films at temperatures from 500.degree. to 600.degree. C. would allow for controlled incorporation of phosphorus from TMPI as well as boron doping from trimethylborate (TMB).
The chemistry of the siloxanes is well developed, see e.g. article entitled "Silicones" in Kirk-Othmer, ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY. While there are some variations in the terminology used to describe the siloxanes, the present description of compounds of the formula EQU (H.sub.n R.sub.2-n SiO).sub.m
wherein n=0-2, and m is 3 or greater, and R is lower 1-8 carbon alkyl, aryl or aralkyl, is consistent with commonly used rules of nomenclature. Siloxanes and polymers thereof, frequently called silicones, have found application in a great variety of industries and for a wide array of purposes in industry, medicine, the arts and in the household.
Siloxanes are used in the semiconductor and electronics industry, principally as silicone potting, shock absorbing, or coating materials, and in masks used in manufacturing of semiconductors. A process for forming a doped oxide film and a composite article by modifying polysiloxane with a dopant, coating the mixture on a substrate and heating coated substrate to diffuse the dopant onto the substrate is described in U.S. Pat. Nos. 4,605,450, 4,571,366 and 4,619,719, wherein a silicon tetra-alkoxide is reacted with a limited amount of water to produce a low molecular weight, soluble polyorganosiloxane. The polyorganosiloxane is subsequently admixed with a reactive dopant source to form a soluble metallosiloxane polymer. The metallosiloxane polymer is coated onto a semiconductor wafer substrate material to produce a metallosiloxane-wafer composite article. The composite article is heated to produce an impurity doped semiconductor wafer suitable for electronic applications. U.S. Pat. No. 4,168,330 to Kaganowicz discloses the use of some siloxanes in the deposition of silicon oxides by glow discharge at low temperatures. Insofar as is known, however, siloxanes have not been thermally decomposed at elevated temperatures to form SiO.sub.2 coatings or layers in the manufacture of semiconductors.